The present invention relates to a pump arrangement for a liquid tank, as used in particular for windscreen washer systems of motor vehicles, boats, trains and ships. In particular, the present invention relates to a pump arrangement having an integrated liquid-level detector with which a critical liquid level in the liquid tank can be detected.
Windscreen washer systems in particular for motor vehicles, which have pump arrangements as an integral part, are known in the prior art. Windscreen washer systems usually consist of a liquid tank (normally made of plastic), a pump arrangement, a nozzle and connecting lines which connect the tank, the pump arrangement and nozzle to one another. If an operator actuates the windscreen washer system, the pump arrangement draws or pumps liquid out of the liquid tank and forces this liquid through the connecting lines towards the nozzle, from which the liquid issues and wets the windscreen.
For some time, such windscreen washer system have also been provided with a liquid-level detector which monitors the liquid level in the liquid tank. If the liquid level in the liquid tank falls below a predetermined minimum level, the liquid-level detector initiates a warning signal. The operator will realize from this warning signal (which may be optical or acoustic) that the liquid level in the liquid tank has fallen below a critical measure and is to be brought up to the full level again, if possible immediately.
Essentially two proposals as to how the liquid-level detector is preferably to be attached to the liquid tank have been made hitherto in the prior art.
According to the first approach to achieving a solution (for example described in Spanish Patent Application P 90 00 819), the liquid-level detector is attached to the liquid tank independently of the pump arrangement. The sensors (electrodes) project into the liquid tank and detect the level there. If the level falls below a predetermined measure, this leads to a voltage drop at the electrodes, as a result of which the warning signal is initiated.
However, this previously known technique has the disadvantage that it may lead to unsteady or intermittent sensor signals as a result of wave motions in the liquid tank. These wave motions may lead to the warning signal being initiated briefly, even though the level in the liquid tank has still not fallen to the critical measure. In order to take this effect into account, the use of electronic logic circuits have been considered, which release the warning signal only when a certain sequence of sensor-signal events has occurred. This leads to increased costs for the entire arrangement. The fact that two electric lines for the pump arrangement and the liquid-level detector, which are provided separately, have to be provided leads to an additional increase in costs.
According to a further previously known approach to achieving a solution, as described, for example, in EP 0 511 352 A1, the liquid-level detector is designed to be an integral part of the pump arrangement. This previously known pump arrangement contains, on the one hand, a pump housing and, on the other hand, an integrated sensor housing in which the liquid-level detector is accommodated. The sensor housing has an inlet and an outlet, which are arranged in such a way that liquid can enter the sensor housing, and the level in the sensor housing corresponds to the level in the liquid tank. The outlet of the sensor housing merges into the inlet of the pump housing, via which inlet the pump arrangement draws the liquid out of the liquid tank. With such an arrangement, it is possible to counter the disadvantages described above, since the liquid-level detector no longer measures the liquid level in the (main) liquid tank but in the very much smaller sensor housing, in which the wave motion of the liquid only has a considerably damped effect.
However, such an arrangement has the disadvantage that it is always expensive to produce. Due to the fact that the sensor housing exchanges liquid directly with the inlet of the pump housing (i.e. merges into this inlet), it is necessary to provide a valve mechanism between the sensor housing and the pump housing, otherwise liquid will be forced into the sensor housing when the pump turbine located in the liquid inlet of the pump housing is actuated. This leads to an undesirable second liquid path, which impairs the mode of action of the pump arrangement.
Another pump arrangement is known from the prior art document DE 37 30 006. The described arrangement comprises a pump housing and a sensor housing attached thereto. According to this prior art approach, the inlet of the pump housing and outlet of the sensor housing are arranged parallel to each other in a common connection piece. This arrangement serves the purpose to allow an assembling of the pump arrangement close to the liquid tank. The disadvantage of this arrangement is, however, that the cross section of the sensor housing outlet in the common connection piece is very small and may be detrimentally effected by impurities in the windshield water. Simply increasing the diameter thereof, on the other hand, would either increase the circular diameter of the connecting piece, or lead to a non-circular connecting piece. Both alternatives are, however, undesired because an increased circular diameter leads to a considerable increase of the wall thickness of the connecting piece, with a related waste of material. A non-circular connecting piece, on the other hand, is difficult to seal with respect to the liquid tank.
Consequently, the technical problem of the present invention is to provide a pump arrangement which, on the one hand, is of simple construction and is therefore inexpensive to produce and, on the other hand, permits precise measurement of the level in the liquid tank.
The solution to the above problem is achieved according to the present invention in its widest approach by a pump arrangement which has a pump housing and an integrated, separate sensor housing.
To put it more precisely, the solution results from a pump arrangement according to patent Claim 1, namely a pump arrangement, in particular for windscreen washer systems of motor vehicles, which comprises:
a. a pump housing in which a liquid-delivery device and a drive device functionally connected to it are provided, the pump housing having
a1. a liquid inlet through which the said liquid-delivery device delivers the liquid, to be delivered, into the pump housing; and
a2. a liquid outlet through which the said liquid-delivery device delivers the liquid, to be delivered, out of the pump housing;
b. a sensor housing which is connected to the pump housing and in which a sensor arrangement is provided which responds to a changing liquid level in the sensor housing, the sensor housing having
b1. a liquid inlet through which liquid can enter the sensor housing; and
b2. a liquid outlet through which the said liquid can issue from the sensor housing; characterized in that
c. the liquid outlet (46) of the sensor housing (40) and the liquid inlet (36) of the pump housing (30) are co-axially arranged with respect to each other, so that the throughflow path of the liquid through the liquid outlet of the sensor housing and the throughflow path of the liquid through the liquid inlet of the pump housing are spatially separated from one another.
Accordingly, the pump arrangement according to the invention solves the problem of the invention in particular owing to the fact that the liquid outlet of the sensor housing and the liquid inlet of the pump housing are co-axially arranged, to run spatially separated from one another.
Such an arrangement has the advantage that a valve arrangement between the sensor housing and the pump housing is no longer necessary; the liquid path of the sensor device is separate from the liquid path of the pump device. Further, due to the co-axial arrangement, the liquid delivery device (usually a suction spindle) is provided in a separate sub-housing allowing a very easy replacement of a spare liquid delivery device in the protective sub-housing, which does not require a difficult alignment of the spindle within the connection piece.
In the pump arrangements according to Claims 2 and 3, in each case either the liquid inlet of the pump housing may be arranged inside the liquid outlet of the sensor housing or the liquid outlet of the sensor housing may be arranged inside the liquid inlet of the pump housing. The geometry selected depends on the given conditions and in particular on the shaping of the liquid tank. At the same time, simple installation of the pump arrangement according to the invention is possible, since this pump arrangement only has to be connected to the liquid tank by means of two connection pieces (the liquid inlet of the sensor housing and the combined liquid inlet of the pump housing/liquid outlet of the sensor housing). In this connection, it may be pointed out that the throughflow paths of the sensor-housing outlet and the pump-housing inlet need not necessarily have a common axis of symmetry. It is also conceivable for the outlet of the sensor housing and the inlet of the pump housing to have a differently shaped cross-section (for example round and elliptical). It is important that separation of the throughflow paths inside the pump arrangement is achieved.
The pump arrangement according to Patent Claim 4 has the special advantage that, due to the different axial length of the (concentric) liquid inlets and outlets, further separation of the throughflow paths is achieved, since the liquid inlet of the pump housing acts on liquid layers of a horizontal plane which is different from that of the outlet of the detector housing.
The pump arrangement according to Patent Claims 5 and 6 has the special advantage that the pump efficiency can surprisingly be increased to a considerable extent. An optimized delivery output becomes possible due to the clearance of the axial suction spindle inside the liquid inlet of the pump housing. The inventors of the present invention have carried out tests and have discovered that the pump does not work perfectly when the suction spindle lies exactly on the axial longitudinal axis of the liquid inlet.
The pump arrangements according to Claims 7 and 8 describe the two embodiments of the present invention which are preferred at present. In the pump arrangement according to Claim 7, the sensor arrangement consist of two electrodes which run essentially parallel to one another and to which a voltage is applied. The voltage drop between the two electrodes depends on whether there is liquid between the electrodes. If the level in the sensor housing falls in such a way that there is no longer any liquid between the sensors, this leads to an increase in the voltage drop, which increase initiates the warning signal. If the liquid level is such that there is liquid between the electrodes, the voltage drop is slight; no warning signal is emitted. Such a pump arrangement has the advantage that it is especially simple and therefore inexpensive to realize, and works reliably.
In the pump arrangement according to Claim 8, the sensor arrangement consists of a float movable in the sensor housing. The float is provided with a first contact element and interacts with a second contact element, in a fixed position relative to the sensor chamber, if the level in the sensor chamber falls to the critical measure.